Stealth, as it applies to radar systems, refers to the minimization of one's radar cross-section. Currently, most stealth systems in development or production are based upon passive, or absorptive approaches, where specialized structural design methods are combined with the use of microwave absorptive coatings. Although success has been achieved with this method, there are still a great deal of problems. Often, the structural design having the smallest radar cross-section will not be the most efficient aerodynamic design, thereby diminishing the performance characteristics of the aircraft. Similarly, while structural design methods are effective in reducing the cross-section of relatively small systems such as an aircraft, they become impractical when attempting to reduce the radar cross-section of something significantly larger and more geometrically complicated, such as a ship. Furthermore, there can still be a significant amount of RF energy reflected from the absorptive coatings.
An active radar stealth technique, known as electronic counter measure (ECM), involves active manipulation of RF signals. However, current systems are limited by the physical properties of metallic based antennae and structures. In these systems the incoming RF signal will be reflected from the metallic skin of the aircraft/ship before an active device on the aircraft/ship can modify the signal and manipulate it or repeat it back to the source. Thus, there is no opportunity for stealth, although there can be cover and deception.